Mechanisms

Levers, pulleys, gears, cams and linkages: how mechanisms change force and movement. Read one part at a time and tap “I know this”. Then test yourself in the quiz.

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Levers and gears

The fulcrum is the point the lever turns about; the effort is the force you put in.

The gear ratio compares the teeth on the two gears.

A crowbar, a lever under a lid’s rim and a spanner are levers. Hold a spanner at the far end.
Three gears in a row: A clockwise → B anticlockwise → C clockwise again.
A sprocket is a toothed wheel that drives a chain, as on a bicycle.

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Pulleys, linkages and machines

Mechanism	What it does	Example
Pulley	Changes direction; lifts a load more easily. The groove stops the rope slipping off	Flagpole; block and tackle
Linkage	Rods joined at pivots	A car’s windscreen wipers
Reverse-motion linkage	The output moves the opposite way	Toy grabber
Car jack	Increases the force	Lifts a car by hand

Input, process and output of a hand winch at a well.

A complex machine is built from simple mechanisms. A bicycle has cranks, a chain with sprockets and levers (brakes). A tower crane uses pulleys, gears and a winding drum. Lubricate a mechanism to reduce friction.

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Remember this and test yourself

Remember this: your summary

A mechanism changes the direction, motion, speed or size of a force.
Move the fulcrum closer to the load for more lifting force; a long arm needs less effort.
A big gear driving a small gear: the small one turns faster; meshed gears turn in opposite directions.
Cam and follower and crank and slider change turning into straight-line motion.
You never get energy for free: more force means less speed and a longer distance.

Write these points in your book. Read them again the night before the test.

Memory trick

More force = less speed. A mechanism is a swap, not a gift.

Flash cards · Tap to turn over

Important words

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Test yourself · Part 2

True or false?

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